S Rank:
S Rank

Gholdengo
S- Rank

Chi-Yu
Dragapult Clear Body and Infiltrator each have their uses on different sets, so having both at once can be good sometimes. Cursed Body is there too, and is always annoying.

Great Tusk
A Rank:
A+ Rank
Annihilape Actually arguably worse, since Inner Focus prevents Defiant from activating off of Intimidate and Vital Spirit is pretty situational. It should still be an incredible mon though.

Chien-Pao
Cyclizar Shed skin + Regenerator is a pretty good combo, and lets you bring Cyclizar even more freely into status spreaders like Rotom-W.
Dragonite Intimidate immunity is nice but pretty situational, since the best Intimidate mons aren't checks to Dragonite really either way.
Espathra Opportunist is a pretty powerful ability, but you need to play pretty aggressively with your Espathra to get the most use out of it. At the least it makes it win CM wars even easier. A good potential use of it is to bring it in on opposing Espathra to dissuade setup.

Iron Valiant
Kingambit Defiant is excellent on top of Supreme Overlord to rule out Tauros-Paldea as an effective check. Kingambit is even better on Sticky Web since it can still benefit if it gets bounced back by Hatterene or Defogged and it appreciates the opposing team being slowed down.

Roaring Moon

Ting-Lu
A Rank
Corviknight Mirror Armor will usually just bounce back Shadow Ball drops, but it's helpful anyways. Unnerve also exists to prevent Rabsca from eating its Leppa Berry.
Dondozo Actually gets some pretty nice buffs. Water Veil lets it come in on Tauros-Paldea and Skeledirge easier, and Oblivious prevents it from being Taunted by Annihilape which really helps that matchup actually. Grimmsnarl is another relevant Taunter that you can turn into setup fodder.
Garganacl Clear Body will help you shut down Shadow Ball even more, or random Intimidates. Sturdy will rarely come in handy on such a bulky mon but is something to consider.
Glimmora Corrosion is pretty niche since you can't Toxic Gholdengo anyways. Glimmora doesn't like running Sludge Bomb much, but it does help that move sometimes.
Grimmsnarl With Frisk and Prankster Parting Shot, Grimmsnarl is an awesome scout.

Iron Treads
A- Rank
Amoonguss Effect Spore is very useful and will help it punish contact attackers like Basculin, Roaring Moon, and others.
Clodsire Three useful abilities. At the same time it's kinda easier to play against because you don't need to guess whether or not it has Water Absorb.
Garchomp Sand Veil is annoying but will hardly come into play unless you build around it.
Hatterene I think the best use of Anticipation could be scouting Iron Valiant for Shadow Ball?

Iron Moth

Rotom-Wash
Skeledirge Blaze is nice since Skeledirge has the bulk to take a hit and activate it, but pretty niche.
Volcarona Swarm and Flame Body are both niche abilities, but Volcarona has made use of both in the past, so it's considerable.
B Rank:
B+ Rank
Baxcalibur Ice Body is only really relevant on teams with Slowking and generally won't make a difference.
Breloom I think Toxic Orb is still a noob trap, even with Technician as well. Unless the meta somehow ends up in a very bulky state, something like Sash or CB seems much better.

Iron Hands
Quaquaval Torrent definitely comes in handy sometimes, especially on a set with Sub or Roost.
Scizor Swarm is situationally useful to power up U-turn.
Slowking Preventing Taunt from Grimmsnarl could help once in a while.
Torkoal Not being crit will pay off over many games.
B Rank
Azumarill Well, now it outright counters Breloom and Meowscarada and is a lot easier to bring in on Chi-Yu and Chien-Pao which is perhaps the most relevant part. At the same time it faces new threats like the buffed Clodsire, but Azumarill is still maybe one of the most improved mons on this list.
Blissey Serene Grace is too niche to build around, only relevant if you run Shadow Ball.
Ditto It has Limber now.
Meowscarada Overgrow can be relevant, but I've also seen sets that don't even run Flower Trick
Pawmot Another mon with three situational abilities. I think Natural Cure and Volt Absorb improve the Rotom-W matchup most of all, but Natural Cure is just useful to have if Toxic Spikes are up.
Toxapex Merciless comes in handy more than you think, since Toxapex is a lot more reliant on Toxic / poison now, but it still doesn't improve your offense much. Limber is also there and situational.
Tyranitar Unnerve lets you counter Leppa Berry Rabsca. Hooray!
B- Rank
Gyarados Intimidate and Moxie are both nice to set up and sweep respectively.
Hawlucha Some nice buffs here. Mold Breaker lets you bust through Dondozo, Skeledirge, and full HP Dragonite. Limber saves you from the rare Thunder Wave Grimmsnarl.
Hippowdon Hippowdon still faces a lot of competition as a bulky Ground, but Sand Force gives it a lot more offensive presence, although it's still pretty passive in the face of Corviknight.

Iron Jugulis
Orthworm Sand Veil is niche unless you build around it.
Pelipper Rain Dish is very nice with Drizzle, but Pelipper is often pivoting out anyways, so it's not as relevant as you'd think.

Slither Wing
Tauros-Paldea-Fire Running a Berry seems pretty suboptimal, even with Cud Chew. Overall I think this mon suffers a bit, as there's a lot more mons with ways to punish or nullify Intimidate in this.
C Rank:
C+ Rank
Barraskewda Propeller Tail is useless in Singles.

Iron Thorns
Masquerain Another counter to Leppa Berry, YES!
Pincurchin Lightning Rod is not a bad ability, but you don't really use Pincurchin for its ability to switch in on things anyways.
Scovillain Banned as it has Moody.
C Rank
Alomomola Hydration is useful for a defensive mon, but I would not run Alomomola on a rain team. Maybe with Rain Dance to self-heal? Still probably bad.
Arcanine Flash Fire is usable to come in on Chi-Yu.
Avalugg Ice Body isn't relevant in general.
Ceruledge Again, Flash Fire lets you dissuade choiced Chi-Yu.
Chansey Doesn't use Serene Grace well.
Charizard Blaze can power you up even more with Solar Power chip, but it's still barely relevant over Chi-Yu.
Cloyster Some niche benefits like hard-switching into Spore, avoiding crits while setting up, not being chipped by sand.
Floatzel Water Veil lets you bring it in on Fire-type burn spreaders, but those won't pose much of a threat to your rain team anyways.
Gallade Justified is useful sometimes, but not much.
Gastrodon Sticky Hold is relevant against Trick users like Gholdengo, as well as weaker Knock Off users, and retaining a Water immunity while doing so is great. Sand Force is probably not worth building around.

Hydreigon
Lokix Take hazard damage to get into Swarm range and revenge kill even better.
Magnezone While trapping feels less relevant this generation, Magnezone is still a beast with its Analytic + Sturdy combo making it relevant in many situations. Sturdy lets it keep pace against offensive teams, and Analytic often lets it secure a revenge kill. Because of this, Magnezone can almost always trade 1 for 1 at least.

Mimikyu
Polteageist Cursed Body lets you cheese some situations.

Scream Tail
Slowbro Slowbro doesn't benefit from Oblivious as much as Slowking since it doesn't have a pivot move to taunt.
Sylveon Cute Charm is the situational sort of thing to punish a Cyclizar going for Knock Off or something.
Talonflame Having Gale Wings on the support set lets you get a fast Defog or potentially revenge kill once with Brave Bird. It's a pretty nice buff for this mon overall.
D Rank:
D Rank

Brute Bonnet
Cetitan Some pretty substantial buffs here, actually. Thick Fat enables you to set up easier, and Sheer Force is a great buff to the power of Icicle Crash. Most notably, it will always OHKO phys def Corviknight at +6, which is probably the most common bulky mon you can encounter that isn't weak to Ice or EQ. The existence of bulky Unaware mons still puts Cetitan out of the limelight, but on paper this is a pretty big improvement.

Gengar
Haxorus Unnerve is almost useless, and Rivalry could hurt you as often as it helps. Overall it's arguably a net negative.
Indeedee Synchronize helps sometimes.
Kilowattrel Wind Power is still probably not worth building around, and Competitive is still pretty niche, so overall Volt Absorb will be the most relevant thing here, still.
Klefki Magician is not really worth building around. It could help if you eat a Knock Off.
Maushold Cheek Pouch is cute but it needs a Wide Lens to function.
Quagsire Pretty good actually. A phys def water immune is useful for Dondozo, Quaquaval, etc. Unfortunately it does not stop Basculin, but it's still pretty good.
Rabsca Telepathy is useless in singles.

Rotom-Heat
Salamence Intimidate and Moxie are nice for a sweeper, but Salamence still faces some strong competition from other sweepers with more optimized stats or better typings.

Sandy Shocks
Umbreon Inner Focus is basically useless, but it's nice to occasionally dodge a flinch.